Moreover, Firefox translation only supports 10 languages, and other 7 languages that’s still in development. Therefore, it isn’t usable for most people (yet), including mine.
I use Brave for webpage translation, which supports 109 languages (Lingvanex). According to their docs, Brave removes IP addresses associated with requests submitted to the translation service and any text submitted is not retained after the request completes. I think this is the best option, privacy-wise. But it’s noticeably slower than Chrome’s Google Translate.
For other use cases, LibreTranslate could be a good candidate. It supports self-host and offline translation.